Added ability to get incoming headers

Fixes #1958: `beforeSubmit` in `yii.activeform` is now executed after validation and before form submission

Transfer beforeSubmit function after global validation all fields forms

Conflicts:
	apps/basic/tests/README.md
	apps/basic/tests/unit/models/LoginFormTest.php

Greek core translation

fixes #1864

Minor fixes in active-record.md

require a version that contains phpDocumentor/Reflection#16

Advanced application template typo fix

added possibility to save messages to be translated

Best way to get the labels to search, the existing model.

Fixes #2016: removed ability to declare scopes in ActiveRecord leaving it to ActiveQuery

Conflicts:
	tests/unit/data/ar/elasticsearch/Customer.php

fixes #1585

fixes #1884

fixes #1905